Outlook will not open

Start Classic Outlook in Safe Mode; if it opens there, disable its COM add-ins because an add-in is preventing normal startup.

Since restarting Outlook did not help, proceed as follows.

1. Start Outlook without add-ins

1. Press Windows key + R.
2. Enter: Outlook /safe
3. Select OK.
4. If Choose Profile appears, accept the default profile and select OK.

If Outlook opens:

1. Go to File → Options → Add-ins.
2. At the bottom, set Manage to COM Add-ins, then select Go.
3. Record or screenshot the currently enabled add-ins.
4. Clear every checkbox and select OK. Disable them—do not use Remove.
5. Select File → Exit, then open Outlook normally.
6. If it now works, re-enable add-ins one at a time, restarting Outlook after each one. Leave the add-in that causes the failure disabled. ^1^

2. If Safe Mode also does nothing, create a new Outlook profile

Because email synchronization stopped immediately before the startup failure, testing a fresh profile is the next useful check; that sequence alone does not establish that the existing profile is corrupted.

1. Close Outlook.
2. Open Start, search for Control Panel, and open it.
3. Select User Accounts → Mail → Show Profiles.
4. Select Add, enter a new profile name, and select OK.
5. Add your email account when prompted.
6. Select Prompt for a profile to be used.
7. Start Outlook and choose the new profile.

If Outlook starts and synchronizes in the new profile, continue using it. Do not remove the old profile until any locally stored data has been backed up; removing it deletes its offline cached content. [^2^](https://support.microsoft.com/outlook/classic-outlook-not-responding-stuck-at-processing-stopped-working-or-freezes#step-5-repair-your-outlook-data-files "Classic Outlook not responding, stuck at "Processing," stopped working, or freezes | Microsoft Support")

3. If a new profile does not resolve it

Try these remaining recovery actions in order:

1. Reset the navigation pane
   • Press Windows key + R.
   • Enter Outlook.exe /resetnavpane.
   • Select OK.
     This removes navigation-pane customizations. ^1^
2. Repair the Outlook data file
   • Close Outlook.
   • Run the installed Inbox Repair Tool (SCANPST.EXE) against the affected .pst or .ost file. Microsoft documents this tool for scanning Outlook data files and repairing detected errors. [^2^](https://support.microsoft.com/outlook/classic-outlook-not-responding-stuck-at-processing-stopped-working-or-freezes#step-5-repair-your-outlook-data-files "Classic Outlook not responding, stuck at "Processing," stopped working, or freezes | Microsoft Support")
3. Repair Microsoft 365 or Office
   • Windows 11: Right-click Start → Installed apps → Microsoft 365/Office → … → Modify.
   • Windows 10: Right-click Start → Apps and Features → Microsoft 365/Office → Modify.
   • Run Quick Repair first.
   • If Outlook still will not open, repeat the process and select Online Repair → Repair. Online Repair is more comprehensive and repairs the entire Office suite. ^3^

References

1. I can’t start Microsoft Outlook or receive the error “Cannot start Microsoft Outlook. Cannot open the Outlook Window” | Microsoft Support
2. Classic Outlook not responding, stuck at "Processing," stopped working, or freezes | Microsoft Support
3. Repair an Office application